This invention relates to certain vinylbenzyl thymine (VBT) monomers and polymers. More particularly, it relates to a class of polymerizable vinylbenzyl (and vinylphenyl) monomers having pendant functional thymine (and uracil) groups useful in the production of polymeric coatings and articles, including photoresists, which can be imaged by a photolytic (crosslinking) reaction.
As used herein, and except as otherwise indicated, the recitations "VBT" and "VBT monomer(s)" are sometimes used to refer to a class of polymerizable vinylbenzyl (and vinylphenyl) monomers having pendant thymine (or uracil) group. The recitation "VBT" refers also to the specific compound 1-vinylbenzyl thymine. The nature of compounds within the aforementioned class will be apparent from the description which follows, including the formulae and the examples.
Thymine itself and polymers containing thymine units are well known and have been described in numerous patents and other publications. Examples of polymers containing pendant thymine groups include DNA or synthethic polymers such as polyethyleneimine, acrylic esters, acrylamides or poly-lysine and have been described, for example, by M. J. Moghaddam, et al., in Polym. J., 22, 468-476 (1990); by K. Takemoto, et al., in J. Macromol. Sci-Chem., A25 (5-7), 757-765 (1988); by C. G. Overberger, et al., in J. Polym. Sci., Polym. Chem. Ed., 17, 1739-1769 (1979); and by C. G. Overberger, et al., in J. Polym. Sci., Polym. Chem. Ed., 18, 1433-1446 (1980).
Prior to the instant invention, monomers and polymers wherein thymine units are attached to vinylphenyl or vinylbenzyl groups were unknown. It will be appreciated that there will be considerable interest in the (vinylbenzyl)thymine monomer which can be used for the production of a variety of useful polymeric materials. A principal use of the VBT monomer is in the area of photoresist coatings that can be imaged by exposure to UV radiation. Another use of the VBT monomer is as a comonomer in the production of mordant copolymers based upon quaternary compounds, as is described, for example, in the aforementioned U.S. Patent Application of J. Michael Grasshoff, et al. (Attorney Docket No. 7919).
The use of photopolymerization reactions in the printing and graphic arts fields for the production of relief and lithographic printing plates has been well known. Suitable methods of the production of plates for the printing and graphic industries are described, for example, in Neblette's Handbook of Photography And Repography, Seventh Edition, pp. 439-40 (1977). Typically, a monomeric compound on a suitable plate support material will be selectively exposed to a source of light so as to effect a photopolymerization (insolubilization) in exposed areas. The difference in solubility, between unexposed and exposed (polymerized) areas, permits easy development.
The principles of photopolymerization are also utilized in photoengraving and lithographic plate-making by the use of polymers whose molecules are able to crosslink under the action of light to form a three-dimensional molecular network. Typically, the photo-crosslinked polymer will be insoluble, and will be soluble only in powerful solvent mixtures of the type used in paint stripping. Stencils produced by the photo-crosslinking reaction are images which are highly resistant to commonly used solutions; solvent development is used to remove the original polymer from unexposed areas.
In U.S. Pat. No. 3,081,168 (issued Mar. 12, 1963 to R. M. Leekly et al.) the production of relief plates using polyamides as a preformed polymer is described. Photosensitivity is imparted to the polyamide, which is carried on a support, by including with the polyamide, a photopolymerizable unsaturated compound. Following a selective exposure to light, which induces a decrease in solubility in exposed areas, unexposed areas are removed with a developer. After development, the base material e.g., metal) can be etched by chemical etching or abrasive blast to form a relief image in the base material. If desired, an offset plate can be prepared by coating the photosensitive polyamide composition onto a hydrophilic support. The image obtained upon photoexposure and development will carry an ink and the wet support will resist ink.
In the production of plates by resort to photoreaction chemistry, a reactive and photopolymerizable monomeric compound will oftentimes be employed. The compounds are frequently liquid or in a gaseous form which may hamper efficient handling and the production of coatings suited to photopolymerization. Preformed polymers which are photo-crosslinkable may exhibit limited photo-reactivity or sensitivity. Accordingly, it will be appreciated that there will be application in photosensitive imaging schemes for a polymeric compound which can be conveniently coated from an aqueous medium onto a suitable substrate or carrier material and which can be readily converted, by a chemical modification induced by exposure to irradiation, to an insoluble or hydrophobic material.